Numbers m such that sigma(sigma(m))/m is a square.

Terms

a(0) =1a(1) =15a(2) =50a(3) =100a(4) =168a(5) =1023a(6) =1444a(7) =1470a(8) =1600a(9) =1944a(10) =3179a(11) =3822a(12) =4000a(13) =5120a(14) =5776a(15) =6174a(16) =9025a(17) =10752a(18) =12348a(19) =14440a(20) =15125a(21) =21970a(22) =26250a(23) =28416a(24) =28665a(25) =29127a(26) =37544a(27) =39200a(28) =45630a(29) =47151